1. Field of the Invention
This invention relates to a steam generator of a nuclear power plant and, in particular, to a temporary plug cover for a hole or a port in the steam generator.
2. Description of the Related Art
The prior art references developed as a result of a preliminary patentability search are listed below.
We note at the outset that the search had not developed any references which taken alone or in combination might be considered to anticipate or render obvious the combination of features in the invention. So, the above references are considered as being of secondary interest.
Rusnica, Jr. et al., Weisel et al. and Dooley show various types of plugs for sealing holes or openings in reactor-related apparatuses. However, none have any significant teaching of the features of the present invention.
Wallace et al., Reich, Jr., et al. and Blanco et al. show the use of lead shielding in reactor-related covers or doors. In the patent to Wallace et al., see the language of col. 2 at line 53. In the patent to Reich, Jr. et al., see the language of col. 4 at line 8. The patent to Blanco et al. teaches both lead shielding as well as the use of openings in the shield for the insertion of a camera. See the embodiment of FIGS. 12 and 13 along with the description of col. 4 beginning at line 60.
Japanese Kokai No. 5-172982 to Maekawa provides a teaching in FIG. 4 of a scheme for securing a cover 20 to a steam generator opening using a nut screwed onto what could be a captive bolt in a blind hole anchored in a vessel wall.
The present invention is characterized by three distinct structural features of a cylindrical cover used temporarily to plug an opening in a steam generator. The features are: an integrally formed lead shielding layer; radiation channeling and diffusing ventilation holes; and a mechanical retainer.
The cover is particularly adapted for temporarily closing openings in a steam generator associated with a nuclear power plant. The cover is cylindrically shaped to fit snugly into round openings in the vessel walls, such as man holes, hand holes, inspection ports, and the like, during maintenance.
As disclosed in a first embodiment which is one of three illustrative embodiments, a cylindrical sleeve formed of stainless steel may have a diameter in the range of several inches and include a layer of lead plate shielding on its inner face. The layer of lead plate may have a thickness of two inches or more. An elongated retaining bar is affixed to its outer face. An array of nominally longitudinal vent holes are drilled through the lead plate. Each hole is typically oriented at a 7 to 25 degree angle to the longitudinal axis. This angle depends upon the diameter of the temporary cover used. The angled holes allow ventilation through the lead plate but channel and diffuse radiation that is axial to the plate away from an operator. During maintenance of the steam generator, any handhole or inspection port that is opened is temporarily fitted with a cover of suitable diameter and retained in place by the elongated bar which is anchored to a flange by a lock which engages a slot permanently cut in the elongated bar.
In a second embodiment, the elongated bar is secured directly to a flange of the handhole or the inspection port. In a third embodiment, two of the ventilation holes are enlarged in diameter to allow the insertion of a camera and/or a retrieval tool into the generator.
Other objects and features of the present invention will become apparent from the following detailed description when considered in connection with the accompanying drawings which illustrate preferred embodiments of the present invention.